This invention relates to methods and means for pulling sucker rod strings and more particularly to a separable connector for use in a well in conjunction with a reciprocating pump in the lower portion of the well and a string of sucker rods used in actuating the pump from the surface.
Downhole reciprocating pumps have been used for years within tubing and casing to lift a column of fluid such as crude oil up the well bore to the surface of the earth. These pumps have been actuated by strings of sucker rods which connect the downhole pump to reciprocating walking beam motors at the surface. The downhole pump is typically tubular in shape with an exterior diameter substantially the same as the interior diameter of the tubing or casing. It is inserted into the tubing or casing at the surface with the sucker rod string attached and lowered into the well until it seats upon an internal shoulder of the tubing or casing provided for that purpose. In operation, the sucker rod string reciprocates a piston within the pump. The weight of the column of fluid above the pump keeps the pump seated upon the shoulder. Since the area of the pump piston is significantly less than the cross-sectional area of the pump, the upward lift required to raise the pump piston is significantly less than the downward force of the fluid column acting on the entire pump, therefore the pump is not unseated during normal operation.
Over an extended period of operation, the fluid in the column above the pump corrodes the inner surface of the tubing and deposits precipitates, such as parrafin, thereon. When it is desired to remove the downhole pump from the well, the sucker rod string may be used to lift the pump to the surface. Since the diameter of the pump is significantly greater than that of the internal piston, the weight of the fluid column upon the sucker rods in this operation is greater than the tensile load on the sucker rods in normal operation. Since the outer diameter of the pump is substantially equal to the inner diameter of the tubing, the pump will engage any corrosion scale or parrafin deposited upon the inner surface of tubing as it is raised therein. The downhole pump body will then either strip this scale and parrafin from the inner wall of the tubing, a task for which it is not adapted and which may damage the pump, or the pump body will become stuck in the tubing. To free the stuck pump, the operator must increase the tension on the sucker rod string or rotate the string and attached pump within the tubing, either of which can result in damage to the pump or the tubing.
Recently, fiberglass sucker rods, such as those disclosed in U.S. Pat. Nos. 2,874,937; 2,874,938; and 4,195,691, and abandoned U.S. Application Ser. No. 956,740 referenced in U.S. Pat. No. 4,195,691, and Canadian Pat. No. 1,072,191, based on U.S. Application Ser. No. 576,731, have begun to replace some or all of the steel sucker rods used in a sucker rod string. Although fiberglass sucker rods have significant advantages, including light weight and corrosion resistance, they are easily damaged by twisting. Therefore a stuck pump body connected to a sucker string which includes fiberglass sucker rods cannot be freed by twisting the string and the pump.
It is an object of this invention to provide methods and means for withdrawing sucker rod strings from a well bore.
It is a further object of this invention to provide methods and means for withdrawing a downhole reciprocating pump or a similar tool from a well bore without stripping the tubing with the pump, damaging the pump by using it to strip the tubing, or twisting the sucker rod string to free a pump stuck within the tubing.
It is a further object of this invention to provide methods and means for use with a sucker rod string which includes fiberglass sucker rods which will permit routine operation of a downhole reciprocating pump but which will permit the operator at the surface to separate the sucker rod string from the pump when he so desires.